Preparation of N-phosphonomethyl glycine

ABSTRACT

A herbicidal compound, N-phosphonomethyl glycine is prepared by reacting 1,3,5-tricyanomethyl-hexahydro-1,3,5,-triazine with a dihydrocarbyl hydrogen phosphite in the presence of a catalyst such as a Lewis acid to form an ester of N-phosphonomethylglyconitrile which ester is thereafter hydrolyzed and the desired N-phosphonomethyl glycine is recovered.

United States Patent 1 [111 3,923,877

Barton Dec. 2, 1975 PREPARATION OF 3,799,758 3/1974 Franz 260/5025 N-PHOSPHONOMETHYL GLYCINE [75] Inventor: John Edward Duncan Barton,

Wokingham, England [73] Assignee: Imperial Chemical Industries Limited, London, England [22] Filed: Oct. 11, 1973 [21] Appl. No.: 405,258

[30] Foreign Application Priority Data Nov. 8, 1972 United Kingdom 51442/72 [52] U.S. Cl. 260/502.5; 260/940 [51] Int. Cl. C07F 9/38 [58] Field of Search 260/940, 502.5

[56] References Cited UNITED STATES PATENTS 2,635,112 4/1953 Fields 260/5025 2,844,558 7/1958 Toy ct al....... 260/940 3,134,800 5/1964 Kagan et al 260/5025 3,322,863 5/1967 Rabourn et al. 260/5025 OTHER PUBLICATIONS Wagner et al., Synthetic Organic Chemistry, (1953), pp. 4l24l5.

Gilman et al., Organic Synthesis, Coll. Vol. 1, 2nd ed.. 1941 pp. 355-357.

Johnson et al., J. Am. Chem. Soc, Vol. 46, (1924), pp. 768-774.

Primary Examiner-Joseph E. Evans Attorney, Agent, or FirmCushman, Darby & Cushman [57] ABSTRACT A herbicidal compound, N-phosphonomethyl glycine is prepared by reacting l,3,5-tricyanomethyl-hexahydro-l,3,5,-triazine with a dihydrocarbyl hydrogen phosphite in the presence of a catalyst such as a Lewis acid to form an ester of N-phosphonomethylglyconitrile which ester is thereafter hydrolyzed and the desired N-phosphonomethyl glycine is recovered.

4 Claims, No Drawings lysts which are acid halides derived from carboxylic PREPARATION OF N-PHOSPHONOMETHYL acids include acetyl chloride and propionyl chloride. GLYCINE An example of a carboxylic acid anhydride catalyst is This invention relates to chemical processes and acetic anhydride. When an acid chloride or an acid anmore particularly to a process for making the herbi- 5 hydride is used as the catalyst, the product of the first cidal compound N-phosphonomethylglycine. stage (a) of the reaction may be the N-acyl derivative According to the present invention, there is provided of an ester of N-phosphonomethylglycinonitrile. The a process of preparing the compound N-phosphonome- N-acyl derivative is, however, hydrolyzed to the free thylglycine, having the formula: NH compound during stage (b) of the process of the invention. The ester of the phosphorous acid and the l,3,S-tricyanomethyLhexahydrol ,3 ,S-triazine may be PCH2NHCH2CO2H used in stolchlometric proportions, that is to say, in the ratio of three molar proportions of the ester of the H0 phosphorous acid to one molar proportion of the hexahydrotriazine. Conveniently however, the phosphorous acid ester may be used in excess to provide a solvent or diluent for the reaction.

Stage (a) of the process of the invention may be carried out with or without a diluent or solvent for the reo action. Suitable diluents, if used, include toluene, dioxan, dimethyl sulphoxide and dimethylformamide,

which comprises (a) reacting l,3,5-tricyanomethylhexahydro-l ,3,5-triazine with an ester of phosphorous acid having the formula:

and as mentioned above, an excess of the phosphorous acid ester used in the reaction. The temperature at which stage (a) of the process of the invention is carried out may vary depending for example upon the cat- 1 2 wherem R i R a hydrocarbyl or subsmuted alyst selected, or upon the boiling point of the diluent 'W radlcals m h Presenc? catalyst m used, if any. In general however, a reaction temperaprfsmg hydrogen hahde} a lfewls acld) a carboxyhc ture of from 15 to 100 Celsius is preferred, although acld hahde or a carboxyl'c aCIdFHhYdFIde to form an higher or lower temperatures may be desirable in some ester of N'phosphonomethylglycmommle and (b) circumstances. The product of stage (a) of the process l g ester of the Nphosphonomethyl' of the invention may be isolated by conventional chemgb'cmommlei and recovermg N'phosphonomethylgly' icals methods well known to those skilled in the art. By cine way of example, a typical procedure would be to dilute The procefcs may be Illustrated by the followmg the reaction mixture with water at the end of the reacuon Scheme tion period, make the mixture alkaline by addition of CNCH,\ /CH2CN R'O 0 catalyst RO O N \il \l k /l /PH /PCH2NHCH2CN rlv R20 R20 Cl-l CN HO\W PCH,NHCH2CO2H Hydrolysis In the above scheme, the groups R and R are not insodium hydroxidesolution, and extract the mixture with volved in the reaction (a) between the ester of phosa water-immiscible solvent such as methylene chloride. phorous acid and the 1,3,5-tricyanomethylhexahydro- The methylene chloride extracts could then be distilled l,3,5-triazine, and are removed when the ester of N- to yield the product. The l,3,5-tricyanomethyl-hexahyphosphonomethylglycinonitrile is subjected to hydrolydrol ,3,5-triazine used in the process of the invention is sis (stage b). The nature of the groups R and R is a known compound; its preparation is described, for therefore not critical, although of course groups which example at page 355 of Collective Volume 1 of Organic might interfere with the reactions involved in the pro- Syntheses, Second Edition, published by John Wiley cess of the invention are to be avoided. Conveniently, and Sons. In the latter publication it is referred to under the groups R and R are both aliphatic radicals, of 1 to the name of methyleneiminoacetonitrile. The esters of 6 carbon atoms, optionally substituted by a phenyl phosphorous acid used in the process of the invention group and may be, for example, alkenyl radicals, alkyare also a known class of compounds, of which examnyl radicals, alkyl radicals, or phenylc0ntaining radi ples, such as diethyl phosphite and dimethyl phosphite,

cals such as benzyl. Preferably the groups R and R are are commercially available.

both alkyl radicals of l to 6 carbon atoms. .The second stage (b) of the process of the invention The catalyst used in the process of the invention is is preferably carried out by heating the ester of the N- preferably hydrogen chloride or hydrogen bromide. phosphonomethylglycinonitrile with a concentrated Examples of catalysts comprising a Lewis acid, that is aquq us solution of a mineral acid. Preferred mineral to say, an electron acceptor, include boron trifluoride, acids are hydrochloric acid, and hydrobromic acid,

ferric chloride, and stannic chloride. Examples of catasince these acids are volatile, which permits the N- 3 phosphonomethylglycine to be isolated from the reaction mixture by concentrating the reaction solution and cooling it until the N-phosphonomethylglycine, which is of low solubility in aqueous solution, separates out.

The second stage (b) of the process of the invention may also be carried out by heating the ester of the N- phosphonomethylglycinonitrile with an aqueous, aqueous alcoholic, or alcoholic solution of an alkali, for example sodium or potassium hydroxide. In this case, a metal salt of N-phosphonomethylglycine will be obtained as the product. Further methods of carrying out the hydrolysis of esters of N-phosphonomethylglycinonitrile to N-phosphonomethylglycine will be apparent to those skilled in the art and the above methods are described only by way of example.

Esters of N-phosphonomethylglycinonitrile are new compounds. In another aspect, therefore, the invention provides esters of N-phosphonomethylglycinonitrile having the formula:

RIO\TI) PCH2NHCH,CN

wherein R and R are each hydrocarbyl or substituted hydrocarbyl groups, useful as intermediates in the synthesis of N-phosphonomethylglycine.

N-Phosphonomethylglycine, as disclosed in Belgian Patent 774,349, is a broad spectrum herbicide having little or no residual effect. Various methods have been proposed for its preparation. Example 14 of US. Pat. No. 3,160,632 for instance, describes the oxidation of glycinemethylene phosphinic acid with mercuric chloride to form N-phosphonomethylglycine. In view of the problems of environmental pollution associated with the use of mercury compounds, this method is obviously unsuitable for large scale manufacturing use. Belgian Pat. No. 774,349 describes the preparation of N- phosphonomethylglycine from glycine and chloromethylphosphonic acid. The chlorine atom in chloromethylphosphonic acid, however, is of low reactivity, and under the forcing conditions required to make the reaction take place, by products are formed, for example by hydrolysis of the chloromethylphosphonic acid. Another by product is the compound formed by reaction of two molar proportions of chloromethylphosphonic acid with one of glycine, that is to say, the compound of structure I-IOCOCH N CH PO H Furthermore this method involves the prior preparation of chloromethylphosphonic acid. The process of the present invention has the advantage that the starting material, l,3,5-tricyanomethylhexahydro-1,3,5-triazine, is readily available from cheap starting materials, namely sodium cyanide, ammonium chloride, and formaldehyde. The phosphorous esters also required as starting materials are also cheaply available.

The invention is illustrated by the following Example.

EXAMPLE This Example illustrates the preparation of N-phosphonomethylglycine by a process according to the invention. 1,3 ,5-Tricyanomethylhexahydro-l ,3 ,S-triazine (10.2g.) dissolved in diethyl phosphite (40 ml; 41.1 g; 100% excess) was stirred and maintained at 40C by cooling while the solution was saturated with hydrogen chloride gas. The passage of hydrogen chloride was then stopped and the mixture, from which a white solid precipitated, was stirred for 1 hour. Water was then added, and the mixture was made basic with sodium hydroxide solution. The mixture was extracted three times with methylene dichloride and the combined extracts dried over magnesium sulphate and evaporated in a vacuum. The residue was distilled and the fraction (1.8 grams) boiling at 148l50C. under a pressure of 0.2 millimeters of mercury was collected. Examination of the infra-red absorption spectrum showed a peak at 3330 cm" assigned to the NH group and a peak at 2250 cm assigned to the CN group. Examination of the product by combined gas liquid chromatography and mass spectrometry showed that it comprised from to 92% of the glycinonitrile derivative of the formula together with from 8 to 10% of a derivative having the formula NCCH N CH P(OC I-I The nuclear magnetic resonance spectrum of a sample of the product in deuteriochloroform was consistent with this structure assignation.

The foregoing product (1.0 g.) was stirred and heated under reflux with 48% hydrobromic acid (6 ml.) for 3 hours. The pale yellow solution was cooled and evaporated in a vacuum. The pale yellow residue was dissolved in a small volume of boiling water (1 to 1.5 ml.). The solution so obtained was filtered and allowed to stand overnight. The white crystals of N-phosphonomethylglycine which separated (0.2 grams) turned yellow at 230C and decomposed at 300C. The infra red spectrum of this material was identical with that of an authentic sample of N-phosphonomethylglycine prepared from chloromethylphosphonic acid and glycine by the method described in Belgian Pat. No. 774,349. The nuclear magnetic resonance spectrum of a sample dissolved in deuterium oxide was also identical with that of an authentic sample of N-phosphonomethylglycine in deuterium oxide.

I claim:

1. A process of preparing the compound N-phosphonomethyl glycine, having the formula:

which comprises (a) reacting 1,3,5-tricyanomethylhexahydro-1,3,5-triazine with an ester of phosphorous acid having the formula:

wherein R' and R are hydrocarbyl or substituted hydrocarbyl radicals in which the substituent is inert to the reaction, at a temperature in the range from 15 to C and in the presence of a catalyst selected from the group consisting of hydrogen halides, Lewis acids, alkanoic-acid halides, and alkanoic acid anhydrides, to

6 form anfistel' of N'Pho5Phonomethylglycinonitrll?, 3. A process according to claim 1 wherein the catarecovermg the ester of N'phosphonomethylglycmom' lyst comprises hydrogen chloride or hydrogen bromide.

trile from the reaction mixture, (c) hydrolysing the ester of the N-phosphonomethylglycinonitrile and (d) recovering N phosphonomethylglycine 5 tron of the l,3,5-tr1cyanomethylhexahydro-l,3,5-tria- 2 A process according to claim 1 wherein the groups zine with the phosphorous ester is carried out in a dilu- R and R each represent an alkyl radical of from 1 to ent comprising an excess of the phosphorous ester. 6 carbon atoms.

4. A process according to claim 1 wherein the reac- 

1. A PROCESS OF PROCESS OF PREPARING THE COMPOUND N-PHOSPHONOMETHYL GLYCINE, HAVING THE FORMULA:
 2. A process according to claim 1 wherein the groups R1 and R2 each represent an alkyl radical of from 1 to 6 carbon atoms.
 3. A process according to claim 1 wherein the catalyst comprises hydrogen chloride or hydrogen bromide.
 4. A process according to claim 1 wherein the reaction of the 1, 3,5-tricyanomethylhexahydro-1,3,5-triazine with the phosphorous ester is carried out in a diluent comprising an excess of the phosphorous ester. 